BS 5950:2000
Provisions of the BS 5950 "Structural use of steelwork in buildings": Part 1, "Code of practice for design: rolled and welded sections" (2000), have been implemented.
BS 5950 Parameters
The implementation of the BS5950-1:2000 requires that the engineer provide additional design criteria. These criteria refer to the type of hollow structural sections to be used on the project, and the height of the restraint of fully braced beam flanges. These criteria are discussed in detail below, but both pieces of information are provided to the program in the Section Properties tab of the BS 5950 Parameters dialog. The dialog is available by selecting the Criteria-BS 5950 Parameters command in the RAM Manager. This command is only available when BS 6399 is selected as the live load reduction code (Criteria – Live Load Reduction). The two values stipulated in this dialog have no impact on the design results performed according to BS 5950-1:1990.
Hollow Structural Sections
BS5950-1:2000 stipulates different design requirements for cold-formed and hot-finished hollow structural sections (HSS). The HSS type affects the classification of the cross section (see table 12 in BS5950-1:2000), and the web shear interaction as described in H.3 of BS5950-1:2000. The engineer can stipulate which type of HSS they are using in the Section Properties tab of the BS5950 Parameters dialog.
Distance to Axis of Restraint
BS5950-1:2000 has changed the method in which the lateral torsional bending capacity of beams is calculated. In certain circumstances, where the tension flange of a beam is fully braced and the compression flange unbraced, the height of the restraint to the tension flange affects the bending capacity of the member (See BS5950-1:2000 4.3.5.3c, Annex G.1. and G.2.). This will typically affect the design of cantilever or continuous members in the zone where the unbraced lower flange is in compression. The engineer can stipulate the distance from the top-of-flange (tension) to the center of the restraint of that flange, in the Section Properties tab of the BS5950 Parameters dialog.
Tables
Three steel tables provided with the program contain the cold-form hollow structural sections. These tables are RAMUK_CF.tab, RAMUK_CF.bms, and RAMUK_CF.col. The RAMUK_CF.tab file includes the section properties of the typical UB and UC sections, and also the properties of the common cold-formed hollow structural sections (HSS). These HSS comply with the requirements of BS EN 10-219. The filename suffix _CF indicates that the HSS designations and properties in these tables are for Cold-Formed sections. These tables do not contain data related to hot-finished hollow sections. The RAMUK_CF.col table contains the same data as the existing RAMUK.col table, except cold-form hollow sections are listed instead of the hot finished sections. The same applies to the RAMUK_CF.bms table.
Bending Capacity
Loads are not considered "destabilizing" per 4.3.4. However, the engineer has the option of supplying the appropriate Le factor per table 13 or 14 in the Criteria-Effective Length dialog box.
For lateral torsional buckling per 4.3.6.7 the u and x term are calculated per B2.3, not 4.3.6.8.
The monosymmetry index, Ψ, is calculated per 4.3.6.7. In the case of highly unsymmetric sections, with values of n outside the range of 0.1 to 0.9, the engineer is responsible for calculating the appropriate buckling capacity.
For channels, loads are assumed to be pass through the shear center per 4.3.6.7b.
G.2. is implemented for I-sections where the tension flange is fully braced and the program is calculating the lateral torsional buckling capacity of the unbraced compression flange. When G.2. is implemented for a beam, the program sets mLT = 1.0 and calculates nt based on the shape of the moment diagram. In the calculation of Mb in section G.2. there is a reference to the distance between the axis of restraint and the axis of the beam. In RAM Structural System, this distance is determined from the distance between top-of-steel and axis-of-restraint, as provided by the engineer in the RAM Manager. This calculation will only apply where the engineer indicates that the top-flange is fully braced. Where the bottom flange is fully braced the dimension is assumed to be half the depth of the beam.